The histological response to a xenogeneic tumour in mice

We have examined, by conventional histological methods, the immune response of normal and ALS-treated mice to a tumour xenograft. In normal mice the histology of the tumour site and lymphoid organs is in agreement with the hypothesis that rejection of tumour is by a cell-mediated response. In ALS-treated mice, lymphoid organs severely depleted of small lymphocytes, show many blast cells which may be responsible for in vitro cytotoxicity. After cessation of ALS there is still a striking lack of infiltrate at the tumour site suggestive of some form of `blocking' mechanism.